RBC transfusion and postoperative length of stay in the hospital or the intensive care unit among patients undergoing coronary artery bypass graft surgery: the effects of confounding factors

BACKROUND: Data on the independent association between perioperative allogeneic blood transfusion (ABT) and postoperative length of stay at the hospital or in the intensive care unit (ICU) are sparse. STUDY DESIGN AND METHODS: The records of 421 consecutive patients undergoing coronary artery bypass graft (CABG) operations at the Massachusetts General Hospital were reviewed. The effect of perioperative ABT in explaining the variation in the postoperative length of stay (LOS) at the hospital or in the ICU was calculated after adjustment for the effects of 20 confounding factors that pertained to severity of illness, difficulty of operation, and risk of postoperative wound infection or pneumonia. RESULTS: Postoperative LOS averaged (mean +/- SE) 8.0 +/- 0.3 days in the hospital and 50.0 +/- 4.1 hours in the ICU. After adjustment for the effects of confounding factors, the postoperative length of hospitalization increased by 0.837 percent (95% CI, 0.249-1.425%) per RBC unit transfused (p<0.001), and the postoperative length of stay in the ICU increased by 0.873 percent (95% CI, -0.068-1.814%) per RBC unit transfused (p<0.10). CONCLUSION: Allogeneic blood transfusion was independently associated with longer postoperative stays in the hospital or the ICU, but the observed independent association is perhaps too small to be clinically relevant. This independent association may be due to a relationship between ABT and a higher incidence of septic complications of surgery, or it may reflect the function of blood transfusion as a surrogate marker for severity of illness.